Source : Webster's Revised Unabridged Dictionary (1913)

Cyclone \Cy"clone\, n.
   1. (Meteor.) In general, a condition of the atmosphere
      characterized by a central area of pressure much lower
      than that of surrounding areas, and a system of winds
      blowing inward and around (clockwise in the southern
      hemisphere and counter-clockwise in the northern); --
      called also a {low-area storm}. It is attended by high
      temperature, moist air, abundant precipitation, and
      clouded sky. The term includes the hurricane, typhoon, and
      tropical storms; it should not be applied to the moderate
      disturbances attending ordinary areas of low pressure nor
      to tornadoes, waterspouts, or ``twisters,'' in which the
      vertical motion is more important than the horizontal.

   2. A tornado. See above, and {Tornado}. [Middle U. S.]

Cyclone \Cy"clone\ (s?"kl?n), n. [Gr.????? moving in a circle,
   p. pr. of ?????, fr. ky`klos circle.] (Meteor.)
   A violent storm, often of vast extent, characterized by high
   winds rotating about a calm center of low atmospheric
   pressure. This center moves onward, often with a velocity of
   twenty or thirty miles an hour.

   Note: The atmospheric disturbance usually accompanying a
         cyclone, marked by an onward moving area of high
         pressure, is called an anticyclone.

Source : WordNet®

cyclone
     n 1: (meteorology) rapid inward circulation of air masses about a
          low-pressure center; circling counterclockwise in the
          northern hemisphere and clockwise in the southern [ant:
          {anticyclone}]
     2: a violent rotating windstorm